To Kill a Waterman
by johnsarmylady
Summary: John meets an old flatmate of Sherlock's, with terrifying results. AU. THIS IS THE SECOND STORY IN THE HELIKEAN SERIES - I recommend you read the first - Taken by the Flood - or this may not make sense. Rated M - Johnlock.


**PART 2 OF THE HELIKEAN SERIES. Recommend you read the first part - Taken by the Flood - or this may not make sense :)**

**Thanks to MapleleafCameo for checking this over for me and finding all my missing comma's.**

It never failed to fascinate Sherlock, the changes in John's body whenever he came in contact with water. To his great delight his flatmate was happy to participate in Sherlock's attempts to learn more – it was tacitly understood that any experiments had to be by mutual agreement – in fact he encouraged Sherlock to learn.

The differences were not purely confined to when he was in water and so they spent time sitting in Sherlock's bedroom, one of only two places they knew themselves to be free of Mycroft's spyware, discussing the aspects of John's physiology that differed from normal – at times it was almost like a game of twister as Sherlock made him twist and turn and bend, contorting his body with ease while he was poked and prodded.

At one point it almost ended in disaster, as John demonstrated his ability to almost bend himself in half backwards. Sherlock chose that moment to poke at the Helikean's flexible ribs – John flipped up into the air like a fish on a line, landing face down on Sherlock's bed, shaking.

"John! Are you okay? What did I do?"

John's fingers flexed, grasping the sheets as the shaking grew more noticeable. Panic rippled through the consulting detective.

"John speak to me!" he carded his fingers through the short blond hair, trying to make sense of the strange noises emanating from his flatmate.

Slowly John raised his head, tears of laughter streaming down his cheek.

"I'm ticklish you daft bugger! Warn me next time." Pulling himself round to sit cross legged on the pillows, a grin still plastered on his face, not bothering to cover his naked body.

"What do you want to try next genius?"

A mobile pinged with an incoming text and Sherlock rolled gracefully to his feet, reaching into his pocket and thumbing the screen open.

"I have a few thoughts, but they'll have to wait – a body's washed up on Wapping Old Stairs."

John was already reaching for his clothes, pulling them on quickly so that he barely kept Sherlock waiting.

Closing the black door behind him, John turned to find a taxi already waiting at the kerbside, Sherlock climbing in and directing the driver to east London.

xXx

Approaching the police tape that cordoned off the pathway between the Town of Ramsgate public house and an old Victorian warehouse conversion, Sherlock and John felt the disdain in Sally Donovan's glare before she even opened her mouth.

"I see we're still offering work to the deluded psycho and the pathetic nobody that follows him around." She spoke to Anderson, but her eyes stayed on the two men walking towards her.

"It makes the DI feel that he's doing his bit for the disadvantaged." The forensic lead replied, turning his back as they ducked under the tape.

"There you see John – I told you there was a reason Lestrade keeps Anderson and Donovan on his team." Sherlock spoke just loudly enough for the two officers to hear.

"Very philanthropic." John replied with a grin as the moved towards the steps and Detective Inspector Lestrade.

"Great, I'm not sure if you can actually help though." Lestrade hopped up the last step and walked towards them. "Body's been in the river for a couple of days, but I'm hoping you can identify him for me."

Glancing over John's shoulder he noticed the twin sour expressions on the faces of his sergeant and his forensic officer.

"What's up with them this time?"

He looked at Sherlock, but John answered.

"Not sure, we were discussing philanthropy and they seemed to get a bit upset."

"Philanthropy?"

"Boring." Flicking up his coat collar Sherlock stomped off towards the water's edge.

Sharing an amused look the doctor and the detective followed him.

They caught him up at the bottom of the steps, where the body had been washed up then dropped by the ebbing tide. He was crouched, carefully avoiding letting his coat touch the body or its immediate surroundings.

"I can't tell you his name," he said standing up and looking up at John. "Recognise him?"

John frowned and stared down at the body. He started to shake his head then paused and took a step closer.

"I wouldn't swear to it, but I'd say he's wearing the same clothes as that bloke who was strangling the prostitute…."

"What? You mean that bloke who was killing girls during…."

"Kinky sex, yes Inspector. What's left of his face is enough to tell me it's the same man; however it's unfortunate but I didn't have the chance to ask him his name as he dragged me into a river in full flood."

"Right," Lestrade waved his people forwards, walking away from the water's edge as he carried on their conversation. "We got a reasonable description of the man from you at the time and from your pimp friend, I was hoping for a bit more…"

"I may be good Lestrade, but I don't do miracles."

"Of course you do – like getting yourself out of that self-same river in full flood." Greg turned a bland stare on the consulting detective before turning and giving John the same look. "As I understand it you dove in after him, John. Care to tell me how the pair of you managed to get out in one piece?"

"Strong swimmer." John said equally blandly. "Mum taught me to swim in open water - rivers, the sea – she wanted to be sure I could look after myself. As it happens, Sherlock's not too shoddy a swimmer either, so between us we managed to get out a little way along the river bank."

"And why the interest now?" Sherlock sneered as he turned his collar up. "You couldn't have asked us this at the time?"

"I hadn't seen the damage a river in flood could do to a body in so short a time," his glance flicked between them again. "Strong swimmers eh?"

John sighed.

"Yes Greg, I pulled off my heaviest clothes – you know this, you returned them – then I dove in after our resident genius." He shrugged. "Admittedly, his clothes weighed him down a little, but with my help he broke surface and between us…"

"Okay, okay" Greg raised his hands in submission. "You make it all sound so easy."

"Well it wasn't, I assure you." Sherlock stared around, bored. "Are we done?"

"Yeah….um…thanks for your help."

"Sorry we couldn't do more." John sympathised as Sherlock brushed past. "I…er… I better catch up with him before he leaves me stranded."

Greg waved him off, not waiting to see where they went.

xXx

Sherlock walked briskly along the road, ignoring the passers-by and ghoulish spectators gathering at the cordon tape, and John had to almost run to keep up.

"Where are we going?" he puffed as he finally came alongside the tall figure in the flapping black coat.

"I know what I want to test next." Sherlock's eyes glowed with unholy delight. "I've noticed that you are considerably stronger in water…"

"Hey, hang on a minute – trying to wrestle me underwater in the bath is hardly a fair test!"

"…so I intend to see how far you can take me underwater, and keep me alive while you do it." He turned down another side alley, far enough away from police operation not to be seen when he reached the water's edge.

"Er, what are you doing?" John watched as Sherlock peeled off his coat.

"John, were you not listening to me?"

"Yeah, but not here and not now! For God's sake we can't just strip off in broad daylight and wander into the water."

Sherlock looked down at him in confusion.

"Look, that water's bloody cold – not that it matters to me, but I won't be able to keep you alive much more than fifteen minutes if you don't wear a dry suit." John looked over the water. "I won't let you kill yourself in the name of research."

"Dry suit?"

"Scuba divers wear them – keeps warmth trapped in, you stay dry, and the likelihood of you developing hypothermia is minimal."

"Right." Doing a smart about-face Sherlock marched away from the river's edge. "Where can I buy one?"

"Whoa, slow down. For a genius you really have no clue, do you?" John shook his head. "We'll get you measured up – I doubt they'll stock them in extra lanky…" He threw his friend an impish grin. "Think of it as an investment – we can attempt grander and crazier experiments once we have you kitted out with the proper gear."

The gleam returned to Sherlock's eyes.

"Come on then John, what are we waiting for?"

xXx

Sherlock ran up the stairs two at a time, clutching a parcel to his chest as if his life depended on it.

"It's here John, it's finally here."

John looked up from his paper.

"My dry suit – I've been waiting…."

"Three days Sherlock, you ordered it three days ago."

"Whatever John, let's go." He whisked away to the bedroom, pulling clothes off as he went.

With a sigh, John folded the paper and put it to one side, following his flatmate at a more leisurely pace. He found him already dressed in the layers of thermal underwear required, and trying to pull on the dry suit.

"Here, let me help."

"What will you wear, John?"

"We'll worry about that tonight." He cocked an eyebrow as Sherlock stared at him. "Less river traffic to worry about; and no one around to see us."

The younger man grumbled but let John assist him as he wriggled into the suit.

"Jesus Sherlock, I could get a serious kink for you in rubber you know." John's mouth went dry and his eyes dilated as he admired the svelte figure.

Sherlock's response was to leer lasciviously down at the blond doctor and back him against the wall, pressing as much of his body as he could against the smaller man, dipping his head to nip gently at thin smiling lips.

"How do you suggest we fill the time then?" grinding his hips against John he continued to steal kisses.

"Later git, first we need to plan exactly how we are going to do this." it took a great deal of willpower for John to pull away. "Now we're sure that fits you properly, take it off and come and sit down – I want you to eat while we map this out…" he didn't miss the scowl that crossed Sherlock's face. "You need fuel to keep your brain active if nothing else, don't waste this chance."

Making good his escape, John hurried to the kitchen to put together a light meal, his mind already working out the best way for conduct this particular experiment.

xXx

Midnight found Sherlock picking the lock on the gate to the now closed Westminster Millennium Pier, and they both slipped through onto the floating deck.

In the shadow of the canopy, they pulled off their outdoor clothes, Sherlock stripping down to his dry suit, John stripping down to his skin. The smaller man carried a large backpack, which they packed their clothes into and stashed in a dark corner.

In Sherlock's backpack there were two large towels, as well as a close-fitting snorkelling mask with an LED torch attached to its strap.

Standing naked and proud in the cloud-veiled moonlight, John checked the seals on Sherlocks suit and checked the torch before turning away and climbing down into the water.

Following him, allowed himself a moment to admire John's muscular physique before turning his mind to the research, his trust in his lover absolute as he took a deep breath and plunged into the murky waters of the Thames.

For thirteen miles John guided him through underwater world that was the River Thames, breathing into him in regular rhythm, and as they slipped further away from central London pointing out the rejuvenation of the ecology of the river. Their journey's end was Richmond Lock – John had already explained that there would be too much machinery to injure themselves on, and no way to pass them without breaking the surface which would effectively end the experiment.

Holding Sherlock captive by pressing him against the lock gate John breathed into him, allowing his body to undulate against the other man, then grinned widely and placed his lips against Sherlock's ear.

"Do you want to break, or return?"

Behind his mask Sherlock rolled his eyes and pointed back the way they had travelled. Return. With a brief nod John brought both feet up beside the consulting detective's rubber clad hips, and slipping his hands under his arms breathed a breath into him before pushing off, undulating against him, using current and momentum to speed through the water, bubbles rising all around them as he laughed out loud for the sheer joy and freedom of this underwater world.

Sherlock marvelled at the sound. Nothing he had ever heard before would compare, and the feeling that it stirred within him was something new and wonderful, yet still the scientists mind noted the difference of the return journey, the effects of their greater speed - which he had estimated to be around thirty miles per hour – and above all that the ripple of muscle against him was doing the strangest things to his stomach.

xXx

The river experiment had given Sherlock much to think about, from the phenomena that was John Watson, a man who exhibited significantly increased stamina and strength the longer he stayed in water, to the possibilities that were opening up to him – crossing the English Channel, the Atlantic – was there anywhere they couldn't travel to unnoticed, arriving under cover of darkness?

John meanwhile had sat back to watch the scientist immerse himself in the information, noting his findings in the notebooks kept secure in his mind palace. His worst nightmare – that he would become a lab rat in some Government installation in the wilds of nowhere – had become a mutual exploration of his abilities, an exploration he and his parents had never dared to undertake, and now here he was, realising his potential at last.

A foolish grin swept across his face as he realised how lucky he was, to have found someone who loved him yet understood and shared his own need to learn more about himself.

"Stop that, it's distracting." Turning his head Sherlock's silver grey eyes gleamed as they roved over the other man's face. "Isn't there something you could be doing other than grinning like an idiot?""

John sprung to his feet and rubbed his hands together.

"Actually, I promised I'd meet Greg for a pint – do you fancy coming?"

A long-fingered pale hand waved him away, an expression of distaste marring his handsome features and he closed his eyes once more.

"Busy." He said shortly, thus closing the matter completely.

Shaking his head, John grabbed his jacket and calling a fond farewell let himself out of the flat.

xXx

Sherlock had managed to ignore the chimes of the incoming texts in favour of compartmentalising his new-found knowledge, but when it rung insistently for the third time he stretched out a hand and answered it irritably.

"Sherlock Holmes."

"Thank fuck you've answered, I was beginning to think the pair of you had vanished off the face of the earth."

"Hardly Lestrade." Sherlock closed his eyes and let his boredom seep into his voice.

"Yeah right, so what wild goose chase have you dragged John off on this time? I mean, I've been waiting at the Albert for the past hour…"

"Say that again." Suddenly Sherlock was alert, his voice suddenly deadly serious.

"John should…" there was a sharp intake of breath as realisation hit. "He's not off doing something for you then?"

"No, he left to meet you."

"How long ago?"

But Sherlock had been in his mind palace, time meant nothing when he was there and he had no idea how long John had been gone.

Greg seemed to pick this up without him vocalising it.

"I assume he was wearing his usual black jacket and jeans, let me arrange a quick check of all the local hospitals while you keep trying his mobile – see if you can track it by its GPS signal." He waited just long enough for Sherlock to agree then ended the call.

Sherlock was already moving towards his laptop, the code for John's GPS readily coming to mind as he powered up and logged on.

His own phone pinged with an incoming e-mail, and he reached for it, not taking his eyes from the rippling search bar of the locater. As it continued to search, he flicked a glance at the message – it was a multi-media message – and when he opened it any thought of tracing John's phone went out of his head.

John stood by the edge of a municipal swimming pool, trussed from head to foot with black yacht rope, and each band of rope threaded with a number of lead diving weights. He was being held upright by two masked heavies.

'_Sherlock, a Mr Moriarty wants to talk to you. He says if you come to meet him tonight, at midnight, at the pool where Carl Powers died, he might not throw me into the water weighted down with close to two hundred kilos of lead…' _

John's voice faltered and his eyes reflected the fear he felt. The camera moved, showing first the blue depths of the pool, and then panned up to James Moriarty's smiling face.

As the small screen went black and then returned to the email list Sherlock stared blindly – John, his John was in the hands of Moriarty, a lunatic who the Holmes brothers had had locked up in Rampton High Security Psychiatric Hospital.

Forcing his mind to concentrate he looked at his watch. Eight twenty five. Three and a half hours, that was all he had to come up with a plan to save John.

He had read real fear on his friend's face, yet he knew being forced underwater would pose no real problem for him. Turning to his laptop he cancelled the search – he knew exactly where John was – and looked up the effects of chlorinated water on gill-bearing aquatic life forms. Ice formed in the pit of his stomach as he read the potential toxic effects of the chemical.

Two things became apparent. The first being that he had to save John no matter what, the second that although his brother would be best placed to help him there was no way he wanted the British Government to learn about his flatmate's secret.

The sound of a car screeching to a halt outside had him grabbing his coat and scarf and running down the stairs. He flung the street door open just as Greg had raised his hand to knock.

"Bloody hell Sherlock, you scared me!" The police officer exclaimed.

"We need to talk." Sherlock herded him back to his car. "But not here – drive us to Scotland Yard." Throwing himself into the passenger seat he waited until Lestrade had pulled out once more into the evening traffic before explaining to him why he needed the older man's promise of discretion and the assistance of the SCO19 firearms unit.

xXx

Eleven forty five, and Lestrade's armed officers were in place.

Shrugging off his Belstaff Sherlock hung it on a hook in the changing room, and then walked out into the main pool area. John was at the far end, looking stoic in the face of his suffering, but Sherlock could read the small signs of stress, see the dark tells of fear in his bright blue eyes. He was still being kept on his feet by the two masked men.

"Moriarty." Sherlock kept his voice even, speaking loud enough to be heard outside of the pool area.

"I knew if I snatched your new friend you'd come running." The cultured Irish voice came from the far end of the room, and as the slender psychopath stepped out from behind his captive Sherlock shuddered at the madness in his eyes.

"You know, you never should have let your brother lock me away Sherlock, that really wasn't nice." He stopped walking about half-way along the length of the pool. "Why did you run to him? We were having such fun."

"Fun?" Sherlock's eyes flickered towards John, then back into the icy dark stare of the madman. "You were murdering people for the hell of it, getting your sick kicks."

"And you were solving the murders, catching the stooges that I set up, you were happy."

He heard John's shocked gasp, but couldn't afford to divert his attention away from the man in front of him.

"And you think that was a good thing to do? James, I thought you were cleverer than that…."

"Oh, but I was cleverer than _you_! You think yourself so clever, but even you didn't know, couldn't tell that it was me and we were _living together at the time!_"

"That was the biggest mistake of my life."

"No!" Moriarty screamed. "You loved me! We were meant to be together!"

"We are complete opposites we always were, but for a brief time I believed you and I could be great, that we could work side by side…."

"And we did!" His face screwed up into a mask of rage he turned, and with a sweep of his hand gave his goons permission to drown the blond doctor. "Until you put me away so you could get yourself a pet…"

John hit the water face first, sinking fast under the weight of the diving leads. He knew the effect chlorine would have at this strength and tried desperately to fight his breathing reflex but it was hopeless, and as his gills opened he felt the chemical burn as his body's survival instinct kicked in.

In the pool area hell was erupting. Sherlock had taken a step towards the water intending to dive in when Moriarty swung back towards him, freeing a gun from his inside pocket and aiming for the consulting detective's head.

Twin explosions echoed around the cavernous room at two SCO19 officers fired, one a headshot, the other a clean shot to the heart. Two more officers took out the hired help, disabling, not killing them.

Kicking off his shoes Sherlock dived, cutting through the water cleanly, swimming down to his stricken friend. At the same time Lestrade burst out of the changing room and dived headlong after him.

Between them they dragged the smaller man to the side of the pool, lifting him out still wrapped in ropes and lead weights.

Ragged choking sounds were coming from his throat, and he twisted and thrashed as he struggled to breathe.

"Lestrade, help me get him to the shower." Sherlock bent to lift his friend's shoulders, but Greg was standing gawping at the fleshy slashes on John's neck.

"For God's sake Lestrade, quickly, he can't breathe, the chemical has paralyzed his gills."

That shook the Detective Inspector out of his stupor and he lifted John's feet. Together they carried him into the changing room and into the shower.

With the water turned on full power Sherlock sat cradling his lover in his arms, letting the water run freely over his face and neck. When it appeared that John still wasn't breathing Sherlock pulled him closer, and leaning down breathed air into the smaller man.

Greg was torn between staring in fascination and keeping the area secure and his officers out. Assuring himself that no-one would enter without permission he retrieved one of several towels from his police issued kit bag and stood watching as John coughed, choked a little and started breathing raggedly.

Tenderly Sherlock continued to hold him, stroking his hand down the side of his face, watching and waiting until coherence returned.

"Who…..?"

"Shh John, later I promise."

Wearily John nodded, lying lax in Sherlock's arms as the two men removed him from the water's spray and untied the ropes.

Sherlock dried John's head and neck, paying extra attention to the sensitive area of his gills, gently patting them until they closed then wrapping him in his Belstaff.

In silence they hurried out to Lestrade's car, the detective handing over the case to the senior SCO19 officer before climbing in himself.

"You lived with him?" John's shaky voice was asking.

"We shared a house at Uni, he was the only one even close to my level, and we….well we met up again years later, I had just got clean…..he offered me a flat share and room to work."

"He was mad, John," Greg added. "When Sherlock was solving those crimes, well you know how Sally always said Sherlock would be the one to put the corpses there? Well she was wrong about that – James Moriarty put them there as a gift, a puzzle for him."

"Mycroft and I – when we realised what he was doing – had him locked away."

"Mycroft?" John groaned as he looked out of the window and saw the black car already waiting outside their house. "What now?"

The car slid to a halt behind the Government car, and Greg looked over his shoulder.

"Your secret's safe with us John – you head straight to bed, we'll deal with his lordship."

With a smile of gratitude and giving Sherlock's hand a quick tired squeeze, John led the way in, heading straight to his room as Sherlock stalked towards his brother, ready to enjoy tearing a strip or two off the British Government for losing so dangerous an inmate – he smiled, preparing to give him hell.


End file.
